The invention relates to a heating set for hair curling rollers, more especially to the electrical heater unit of the heating set serving to transfer heat from resistance heater means to such rollers.
A hair roller heating set generally comprises a box-shaped container which is readily opened and closed and which houses a given number of hair curling rollers. The rollers are heated while positioned on metal posts which form part of a common electric heater unit inside the casing; the rollers are taken out of the casing one by one and placed in the hair with strands of hair wound around them, thus forming the desired curls or waves of the hair-do. As in all electric heating units, the roller heater is provided with temperature controlling means, such as a thermostatic switch, in order not to overheat the rollers, and with switching and back-up temperature limiting.
In order to attain satisfactory operation of the heating set, it is important that every one of the rollers is heated to the same temperature, and that it is heated as rapidly as possible after having been placed onto its respective post. This requires even distribution of heat over the entire heating unit and effective heat transfer from the electric resistance heater to every post and, likewise, from post to roller.
The known roller heating sets comprise heat transfer units which consist either of die-cast aluminum or zinc bodies, or of pressed and stamped metal sheeting. The conventional die-cast unit generally consists of a flat plate with three rows of upwardly extending posts on its top side and with a plurality of narrow ribs on its underside. The ribs form continuous channels serving to have electrical, metal-sheathed heater inserted therein, and to be bent over the heater after its insertion, so as to provide intimate contact between the plate and the sheathed heater.
These units are comparatively expensive owing to the large weight of zinc or aluminum required for a die-cast body. They heat up slowly, again owing to the large mass of zinc or aluminum which has to be heated initially before heat is transferred to the rollers. They are usually provided with a sheathed resistance heater laid in the channels between the ribs in U-shaped arrangement, a system which makes for unequal heat distribution, although the large mass makes somehow up for it. The penalty, as said before, is slow heating-up and high cost.
The known sheet-metal units generally comprise of a first oblong plate perforated in predetermined locations, and deep-drawn posts fastened in the perforations by swaging, for the purpose of rapid heat transfer. The heating element mostly used in these units consists of a central, oblong mica plate wound with resistance wire and positioned between two outer mica plates serving as electrical insulation. The heating element is positioned underneath the first plate and urged towards its underside by a second, separate bottom plate fastened to the first plate by such known means as rivets or screws. The wire is wound upon the central mica plate in a manner concentrating more wire towards the end portions, thus delivering more heat energy to the posts located at the ends of the plate; this arrangement serves to ensure a more or less even distribution of heat to all posts, whereas with uniform heating of the entire surface the posts at both ends would receive less heat energy than those in the central portion of the plate. However, with three parallel rows of posts, as is the general rule, the center row would be more intensely heated than the lateral rows. Another drawback of the location of the heating element is the loss of heat energy by radiation and convection to and through the bottom plate.
Another drawback of the known sheet metal units is their high cost due to the use of separately fabricated plates and posts and their subsequent assembly and connection by swaging.
A method of heating every post--and likewise every roller--to the same temperature by supplying to each to same heat energy is disclosed in U.S. Pat. No. 3,473,005. In a sheet metal heating unit provided with hollow posts, an insulated resistance wire heater of the kind known as "rope heater" extends underneath the sheet metal plate while entering each post from below and being secured therein close to the post's inner surface by special clamps. Each post contains the same length of rope heater of the same ohmage, and it is evident that not only is an equal amount of heat energy supplied to each post but that an excellent heat transfer to the roller is assured due to the closeness of wire and roller material.
The system appears to be theoretically ideal, but the labor involved in inserting the rope heater into every individual post and in securing it therein, results in a very expensive unit, in addition to the cost of the great length of rope heater required.
It is, therefore, the main object of the present invention to provide an electrical heater unit for a hair curler heating set that is of light weight and can be manufactured at low cost.
It is another object to increase the heating effectiveness by providing a rapid heat transfer from a resistance heater to the rollers and by reducing the heat losses by radiation and convection through the bottom as in conventional heater units.
And it is a final object to provide the same heat energy to every one of the posts in the unit, as far as this is possible.